The present invention relates to a control apparatus for a hydraulically operated vehicular transmission comprising a plurality of forward transmission trains which are established respectively by individual hydraulic clutches, a reverse transmission train which shares for common use a hydraulic clutch with one of the forward transmission trains, and a selector device that is switchable to a forward side in which the forward transmission trains are established and to a reverse side in which the reverse transmission train is established.
There has been known, as disclosed in Japanese Pat. Application, Laid-open No. 84450/1986, a control apparatus for a hydraulically operated vehicular transmission wherein, for example, the highest speed forward transmission train and a reverse transmission train share a hydraulic clutch, the highest speed forward transmission train and reverse transmission train are selectively established by a selector device, and a hydraulic circuit equipped with a manual valve switchable to a forward position and to a reverse position is provided with a servo valve for forward/reverse switchover which is connected to the selector device so that when the manual valve is operated for switchover to the reverse position, the servo valve is switched over to a reverse location at which the selector device is set to the reverse side and at the same time oil is supplied to a hydraulic clutch for the highest speed transmission train so as to establish the reverse transmission train.
Here, the servo valve is urged by a spring to the forward location at which the selector device is set to the forward side. When the manual valve is switched over from the reverse position to the neutral or parking position, the servo valve is returned from the reverse location to the forward location by the resilient force of the spring, and the servo valve is bound to be in the forward location by hydraulic pressure as the manual valve is switched over to the forward position.
With the above-described type of the apparatus, there is a problem that a clicking noise occurs when the manual valve is switched over from the reverse position to the neutral or parking position.
The cause for this noise is described below in conjunction with an apparatus of the type in which the common-use hydraulic clutch for the highest speed forward transmission train and the reverse transmission train is provided on the input shaft of the transmission and the selector device is provided on the output shaft of the transmission.
When the servo valve is returned from the reverse location to the forward location by the resilient force of the spring as the manual valve is switched over, there occurs in the course of the switchover a neutral condition in which the sleeve of the selector device is not engaged with the gear of the reverse transmission train nor with the gear of the highest speed forward transmission train. Even when rotation of the output shaft is stopped by braking under such a condition, the input shaft is subjected to no load and thus rotates. The gear of the highest speed forward transmission train is also rotated, via the common-use hydraulic clutch, by the rotation of the input shaft since the common-use clutch is not yet complete disengaged immediately after the switchover of the manual valve whereas the selector device sleeve has stopped rotation as has the output shaft. Consequently, both come to be intermeshed with each other while relatively rotating, so that noise is generated from them striking against each other.
In case where the apparatus has the hydraulic clutch provided on the output shaft and the selector device provided on the input shaft, when the selector device sleeve is moved to the neutral condition, the selector device sleeve rotates together with the input shaft while the gear of the highest speed forward transmission train does not rotate since it is connected through the hydraulic clutch to the output shaft which is stopped from rotating, so that both also come to be intermeshed with each other while relative rotating as in the situation described in the foregoing, and as a result, noise is also generated.
In such a case, one possibility is to employ a synchromesh type selector device for preventing generation of such a noise. However, this results in a high cost problem.
It is, therefore, the first object of the present invention to provide the apparatus which prevents generation of such noise through a partial improvement of the servo valve.
Also, when the manual valve is switched over from the reverse position to the forward position, there is generated a noise for the same reasons as above. In addition, when a vehicle is unable to move out because its driving wheel is caught in a muddy spot, switchover operation of the manual valve from the forward position to the reverse position and vice versa is performed while the accelerator pedal is continually pressed so as to get out of the spot, as occasion demands. In such a case, since the driving wheel is slipping as it revolves, the selector device sleeve and the gear of the highest speed forward transmission train would be compelled to be intermeshed with each other while they are rotating in mutually opposite directions when the servo valve is switched over from the reverse location to the forward location as the manual valve is operated for switchover from the reverse position to the forward position. This causes a revolution speed difference between the two to become greater at the time of their intermeshing and thus results in wear of the intermeshing portions of the gears. It is, therefore, the second object of the present invention to get rid of such drawback.